Author Topic: Regulated Power Supply Circuit design  (Read 15505 times)

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Offline rstofer

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Re: Regulated Power Supply Circuit design
« Reply #25 on: November 05, 2017, 07:43:11 pm »
 

Online Kleinstein

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Re: Regulated Power Supply Circuit design
« Reply #26 on: November 05, 2017, 09:07:01 pm »
Daves Lab supply design videos have some good points, but also some pretty stupid ideas. Using an LM317, LT3080 or similar is not a good starting point to build a lab supply. These are nice chips if you need an adjustable voltage for a well behaved circuit, but they have no adjustable current limit and adding one is like more complicated than the full thing.  If at all use a regulator chip that has provisions for an adjustable current limit, like the L200, lm723.

Dave's LT3080 based lab supply did not really work and the project thus never finished. I doe's not hurt watching the videos, but I would not at all recommend that circuit.

The linked circuit that mariush gave is a very simple standard circuit, maybe a little on the simple side, but reasonably easy to understand.  At low power one can leave out the transformer tap switching.
 

Offline orolo

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Re: Regulated Power Supply Circuit design
« Reply #27 on: November 05, 2017, 09:50:37 pm »
Kleinstein, you are right, but you are also speaking from a professional point of view. For a hobbyist, building equipment is a learning experience, also an imperative. You build a limited LM317/LM337 linear supply, learning a lot (morale boost), and move on to use it for other experiments. You become aware of its limitations, and learn more. Then you decide to build a better supply, and you're ready for it. My first homebrew power supply was a bipolar 317/337 inspired by the Elliot sound page, mains kit ripped from a IBM computer, huge capacitance multiplier included, with a voltage meter taken from a ultracheap chinese analog multimeter. I still use it a lot (I'm not a pro, obviously), though I've upgraded to a 723 design. Using this first supply, I soon learned to detect a short because the transformer started humming and the voltage dropped almost to zero (clack!, the cheap analog meter dropped and bounced). As long as you don't bypass the 317 with transistors, the crude protection is good enough for a beginner.
 

Offline rstofer

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Re: Regulated Power Supply Circuit design
« Reply #28 on: November 05, 2017, 10:52:10 pm »

The linked circuit that mariush gave is a very simple standard circuit, maybe a little on the simple side, but reasonably easy to understand.  At low power one can leave out the transformer tap switching.

Yes, the linked supply circuit is the kind of thing I was talking about when I mentioned op amp control loops and such.  It probably works very well but, in my opinion only, it is over the top for a first hobby PS project.  It's also complex enough that it probably needs a PCB - another stumbling block for newcomers.

I wasn't really recommending Dave's circuit either but Dave's circuit has the advantage that every single aspect is discussed including the bit about referencing the datasheets.  It might be worth building just to follow along - an educational project, not the final solution to power supplies.  A breadboard solution is workable.

One point I did make was something Dave hit on in the first video:  Be realistic with the specs!  It seems that 3A is some kind of a universal constant, something like 'e' or 'pi'.  Everybody wants 3A!  Why?  Same for 30V!
 

Offline hermit

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Re: Regulated Power Supply Circuit design
« Reply #29 on: November 06, 2017, 12:35:32 am »
Is this the series of videos I learned that Microchip seems to have the lowest cost chips?  That there is a wide range between "typical" and the "max" rating?  That Dave seemed to be unlucky enough that all of his chips seemed to fall at the end of the range than near "typical"?  In other words, is this the series I learned that Microchip probably isn't very honest with their "typical" listing?
 

Offline Cliff Matthews

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Re: Regulated Power Supply Circuit design
« Reply #30 on: November 06, 2017, 03:38:01 am »
Maybe if you're stuck with that transformer...
You could add a 10% mains boost switch with an small auto transformer? A 50VA 12v lighting transfo's more than enough for those times when you just have to run up the output. https://www.eevblog.com/forum/beginners/rolling-my-own-boost-auto-transformer-(sort-of-)/msg1284154/
This one's a bit high, but you get the idea..
 

Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #31 on: November 06, 2017, 05:27:48 am »
Thanks a lot, sir...

                 I am a student of Electrical Engineering. can anybody suggest the book for current control in regulated power supply. no book gives the circuit for current control in linear regulated power supply design.
 

Offline rstofer

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Re: Regulated Power Supply Circuit design
« Reply #32 on: November 06, 2017, 05:51:10 am »
Study the linked schematic carefully,  you will see where Q2 is the output pass transistor and Q1 is part of a Darlington arrangement to increase the gain.  Power transistor typically have fairly low gain.

The signal to pass more or less current comes over the connector CN4.  The rest of the upper circuitry is just the transformer winding and the rectifiers.  Below are two fixed voltage supplies.  The center 5V supply controls the relay that selects the transformer voltage and the lower PS provides + and - 5V.

Now for the control loops:  Note that CN4 Pin 2 has is held high (turning the pass transistor on) by R45.  Two things can pull this voltage down.  The upper op amp, IC3A, measures current (see how IS is generated across the 0.1 Ohm resistor)  If it goes higher than the setting on the pot, the op amp output starts to pull the control voltage down through D2.  There's a bit of integration going on in the feedback for the op amp to slow things down.

Voltage control comes from the lower op amp, IC3B, through diode D3.  That long resistor chain comes from both VS- and REF.  It is compared to the voltage setpoint and is the primary control of the signal going to CN4 Pin 2.  IC3B also has a little integration going on to slow things down.  At least I think that's what the capacitor is doing in the feedback path.  I suppose it could also be considered a filter.

So, that's it!  Two control loops, one for current and one for voltage are combined to control the pass transistor.  The rest of the circuitry has to do with warning LEDs and I have no idea what the lower left op amp is doing.  It's too late at night to figure it out.

Regardless of where you come up with a schematic, it will have to accomplish the same thing.  Clearly there needs to be a voltage comparator the drives the pass transistor.  That is basic voltage regulation.  Next, there has to be a way to diminish the drive when the output goes overcurrent.  The rest is just details.
 
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Offline Jwillis

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Re: Regulated Power Supply Circuit design
« Reply #33 on: November 06, 2017, 08:01:58 am »
I'm confused about that transformer 24-0-24 @ 5amp.Is that 5 amps series 48 volt or parallel 24 volt .Also I've also been looking into current control for my Frankenstein PSU and came up with this as an add on.For the CCR I figure a NSI50350AD http://www.onsemi.com/pub/Collateral/NSI45030-D.PDFshould work.   
 
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Offline IanB

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Re: Regulated Power Supply Circuit design
« Reply #34 on: November 06, 2017, 08:05:27 am »
I'm confused about that transformer 24-0-24 @ 5amp.Is that 5 amps series 48 volt or parallel 24 volt.

A 24-0-24 volt transformer is a 48 volt transformer with a center tap (in this case 48 V 5 A). It is not possible to wire a center-tapped transformer like this in parallel. You could only do that if there were two completely separate secondary windings with no connection between them.
 
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Offline Jwillis

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Re: Regulated Power Supply Circuit design
« Reply #35 on: November 06, 2017, 09:08:47 am »
Sorry I'm a beginner.By parallel this is what I mean. 
 

Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #36 on: November 06, 2017, 10:02:42 am »
Sir,
     There is no link attached to it...
 

Offline rstofer

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Re: Regulated Power Supply Circuit design
« Reply #37 on: November 06, 2017, 03:13:35 pm »
I was talking about the schematic embedded in Reply 22
 
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Online Kleinstein

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Re: Regulated Power Supply Circuit design
« Reply #38 on: November 06, 2017, 04:45:56 pm »
I'm confused about that transformer 24-0-24 @ 5amp.Is that 5 amps series 48 volt or parallel 24 volt .Also I've also been looking into current control for my Frankenstein PSU and came up with this as an add on.For the CCR I figure a NSI50350AD http://www.onsemi.com/pub/Collateral/NSI45030-D.PDFshould work.   
That circuit looks like horribly slow  :--. The extra PV optocoupler is a really bad idea for a control loop, that should be relatively fast for a voltage regulator.

For learning about the design of power supplies it is a good idea to look at the Application notes from the big IC companies. A good example is AN1148 from National Semi (now Ti). There are other good ones from Ti and Motorola too. For an EE student they can be understandable, though not always easy.
There is also a rather long explanation on lab supplies from HP. 

The failure of Daves µSupply idea has nothing to do with parts being low quality of not reaching typical performance.  It is more about start with a voltage regulator and trying to add current limiting as an afterthought.
« Last Edit: November 07, 2017, 11:56:37 am by Kleinstein »
 
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Offline Neomys Sapiens

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Re: Regulated Power Supply Circuit design
« Reply #39 on: November 06, 2017, 11:54:05 pm »

One point I did make was something Dave hit on in the first video:  Be realistic with the specs!  It seems that 3A is some kind of a universal constant, something like 'e' or 'pi'.  Everybody wants 3A!  Why?  Same for 30V!

Well, the 30V seem understandable to me, as getting into electronics involves not only circuit experiments, but also playing around with anything interesting and some repair attempts as well. And a lot of industrial things (control and sensor stuff, relays, PLCs and other modules) use 24V DC nominal.
 
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Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #40 on: November 07, 2017, 03:26:32 pm »
Hi to all,

         Thanks to Kleinstein, i went through National istrument document(application Note-28). Thank you sir. today i went through the shop for buying component to test the circuit. but i found difficult in finding Zener diode(Lm113,1N821), Lm395(power transistor), and OPamps. But the application note gives promissing thoughts in getting result. these component were obselete in market. please any body could suggest  alternative component present in today's component to build the circuit.
 Thank you all...
           
 

Online Kleinstein

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Re: Regulated Power Supply Circuit design
« Reply #41 on: November 07, 2017, 03:58:57 pm »
The zeners / refs are rather easy to replay something like TL431 and LM329 would be a possible choice.
For the protected power transistor, a replacement is more difficult. Without the protection just an NPN could do it, but this will not work with 3 in parallel, but just one (Darlington-) transistor. Something like am TIP 140 could be suitable. Parallel connection would need extra resistors. The lower LM395 would need extra current limiting added. In some circuit the LM317 can be used to replace the LM395.

The LM308 could be replaced by a more modern OP - for the LM101, the LM301 (reduced temperature range) is usually possible. With this op the compensation pins are used and thus a replacement difficult. 

Anyway the circuit has some interesting aspects, but is a little unusual.
« Last Edit: November 07, 2017, 04:03:16 pm by Kleinstein »
 
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Online paulca

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Re: Regulated Power Supply Circuit design
« Reply #42 on: November 07, 2017, 04:28:03 pm »
For fixed voltages, a PC PS works well.  It won't have adjustable current limiting so it is more useful for things like motors.  It also provides very high current so the smoke will leak out in a great big hurry!

Sorry to hijack but is there a defacto PC PSU thread on the forum? 

I can find lots of example breakout boards for the ATX supply, but it seems an awful waste to just leave the high amp PCI 12V rails disconnected.  I am thinking of using it as a DC power supply for DC-DC buck/boost Bench power supply type things.
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Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #43 on: November 07, 2017, 05:16:11 pm »
The zeners / refs are rather easy to replay something like TL431 and LM329 would be a possible choice.
For the protected power transistor, a replacement is more difficult. Without the protection just an NPN could do it, but this will not work with 3 in parallel, but just one (Darlington-) transistor. Something like am TIP 140 could be suitable. Parallel connection would need extra resistors. The lower LM395 would need extra current limiting added. In some circuit the LM317 can be used to replace the LM395.

The LM308 could be replaced by a more modern OP - for the LM101, the LM301 (reduced temperature range) is usually possible. With this op the compensation pins are used and thus a replacement difficult. 

Anyway the circuit has some interesting aspects, but is a little unusual.




Sir please suggest some other circuit involving opamp for current regulation. Thank you sir..
« Last Edit: November 07, 2017, 11:59:43 pm by techguru »
 

Offline not1xor1

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Re: Regulated Power Supply Circuit design
« Reply #44 on: November 08, 2017, 06:42:53 am »
The LM308 could be replaced by a more modern OP - for the LM101, the LM301 (reduced temperature range) is usually possible. With this op the compensation pins are used and thus a replacement difficult. 

I always appreciate your posts, but this time you missed a relevant detail  :)

it is not just a matter of temperature range, the LM101 has a lower offset and withstands an higher supply voltage, +/-22V, while the LM301 is not specified for voltages above +/-18V, although real samples may survive nicely since are probably just 101s marked as 301

the supply voltage is already a bit above the limit in the original circuit as 35+10 = 45V

another possible problem is the current limit LED which might get too much current with some other opamp (the LM108 short circuit current is less than 10mA)
« Last Edit: November 08, 2017, 06:56:34 am by not1xor1 »
 
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Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #45 on: November 08, 2017, 05:26:58 pm »
Hi all,
        I have decided to go for building power supply with two transformer for 2 separate channels which could be used to power opamp as well.
now how to place two transformer in same cabinet. Are there any constraint in placing them?.Could you please all help me in this regard...
 

Offline kingoft

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Re: Regulated Power Supply Circuit design
« Reply #46 on: November 08, 2017, 06:24:24 pm »
There is a falacy in using gigantic capacitors to hold up the average voltage and it is related to conduction angle of the rectifiers.

http://www-personal.engin.umd.umich.edu/~fmeral/CIRCUITS/05*Unit%205/Diode%20Rectifiers.pdf

Bottom line:  If the conduction angle is very short, the rectifiers have to deliver the total energy in a short period of time.  The current goes way up!  Of course, the transformer also sees the high peak current and drops its output voltage.

I wonder why anybody wants to go through the anguish of trying to build a PSU when they are dirt cheap:

https://www.banggood.com/DPS3003-32V-3A-Buck-Adjustable-DC-Constant-Voltage-Power-Supply-Module-Integrated-Voltmeter-Ammeter-p-1062475.html

Here's another thread re: DIY power supplies (among other things):
https://www.eevblog.com/forum/beginners/cheap-oscilloscopes-and-psus/

It's real easy to build PSUs based on the 7805,7905,7812 etc.  But these are fixed voltage with built-in current limiting.  Unfortunately, the current limiting can't be set down to a really low number like 100 mA.

The LM317 is a better approach for adjustable supplies but current limiting may take a 2d 317.

Overall, you will wind up with a bunch of op amps around a current loop and voltage loop all working to drive a pass transistor.

Search around this site and the rest of the Internet.  There are a lot of projects and none of them are simple.  Adjustable current limiting is a bit hard to do.

Here's one approach to creating a PSU with current limit.  It is a lightweight PS though, it only delivers 1.5A 0..26V.  But it does serve to show the complexity of a PSU with adjustable voltage and current limiting.

http://dangerousprototypes.com/blog/2014/04/27/app-note-simple-current-limiting-power-supply/

Where does the 3A requirement come from?  Is it just copied from a catalog?  I can't imagine building up a breadboard that needed even 1A, much less 3A.  If I needed more than 3A, I would probably use a purpose bought fixed PS or a set of batteries.  In my corner of the sandbox, 100 mA is a lot!

I do like the idea of adjustable current limiting when I bring up a new project.  It kind of keeps the smoke inside the chips.

For fixed voltages, a PC PS works well.  It won't have adjustable current limiting so it is more useful for things like motors.  It also provides very high current so the smoke will leak out in a great big hurry!

Add a connector:

https://www.sparkfun.com/products/12867

Here's a teardown video of the Rigol DP832.  Ignore the UI components and the CPU/networking and you still have a bunch of parts involved in a 3 output supply.



I was about to post the same thread, thanks to you  :)
EEE Project Ideas for beginners and basic electronics.
 

Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #47 on: November 09, 2017, 01:16:50 am »
Hi my question is what will happen ,if I place two iron core step down transformer adjacent to each other. Or what is the way to place them in same cabinet.
 

Offline techguruTopic starter

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Re: Regulated Power Supply Circuit design
« Reply #48 on: November 10, 2017, 08:59:09 am »
hi to all,

            Can anybody help me in constructing Circuit using L200 IC where i could adjust current as well.Give some prons and cons of L200 IC. Thanks to all of you....
 

Offline tooki

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Re: Regulated Power Supply Circuit design
« Reply #49 on: November 10, 2017, 11:41:31 am »
Hi my question is what will happen ,if I place two iron core step down transformer adjacent to each other. Or what is the way to place them in same cabinet.
Others can correct me if I'm wrong, but I don't think anything will happen. You see this done all the time.

I know that my Keithley 2015 multimeter uses two transformers (one for the multimeter part, one for the DSP board), and my Tascam studio headphone amplifier uses two, I think one each for the positive and negative rails.
 


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